1. Field of the Invention
The invention relates to a process for the compensation of losses of a signal along a transmission path, especially an acoustical transmission path, that is between at least one transmission point and a reception point in a room, particularly within a vehicle's interior.
2. Description of the Related Art
A similar topic is discussed in the simultaneously filed report “Kommunikationsanlage fuer Insassen in einem Fahrzeug” (“Communications' equipment for occupants in a vehicle”), the disclosed matter of this report is included herein by reference. This report has DE file number 19938171.2.
In a vehicle, e.g. in an automobile, the communications between vehicle occupants is degraded because of ambient noise. On the one hand, communications between occupants will be influenced by their seating arrangement. In that case the quality of the communication is especially poor between people sitting in the front and the back of the vehicle due to the speech direction (signal spreading) and the therefrom resulting corresponding signal loss along the transmission path. On the other hand, the communications between the occupants will be affected, for example, by road or wind noise. For improvement of the communications in the interior of the vehicle, anti-noise systems are usually used that reduce all ambient noise, especially motor noise, road noise and fan noise. To this end such anti-noise systems have a microphone, for example near the head of the occupants, that serves to acquire the wide band noise signals. The signal indicating the rotational speed of the engine can serve as an indicator of the engine noise. A loudspeaker will produce a signal that is of opposite phase to the noise signal, a so called anti-noise signal. Such an anti noise system is described, for example, in the article by Garcia-Bonito et al.: “Generation of Zones of Quiet Using a Virtual Microphone Arrangement,” Journal Acoustical Society of America, 1, Jun. 1997, pages 3498 through 3516. A detriment to these systems is that spoken communication among the occupants between acoustically unfavorable positions in the vehicle is further substantially affected.
Additionally, modern vehicles provide a hands-free speaking device for radio telephones, that makes possible communications with a distant participants. With this device the reduction of the ambient noise, such as, for example, audio signals, road noise or fan noise, in the interior of the vehicle is also important for improved communications. Additionally compensated for by such hands-free speaking devices are acoustical and electrical echoes, which likewise substantially affect communications, that occur due to the particularly long signal delays of the telephone network. Echo cancellation is usually used for this. The use by other occupants of the vehicle of the hands-free speech feature is very restricted due to their acoustically disadvantageous position in the vehicle, since the microphone is especially oriented for the driver of the vehicle.